Isocyanate is the most prevalent agent in occupational asthma(OA) in Korea. We analyzed 43 toluene diisocyanate(TDI) induced OA patients of whom 81% were found to be spray painters. The bronchial sensitivity of all subjects was confirmed by TDI-bronchial challenge test. Serum-specific IgE antibodies to isocyanate-human serum albumin(HSA) conjugate were detected by RAST technique(Pharmacia, Sweden). Bronchial challenge test results revealed 21(57%) early, 5 late only, 4 dual, and 12 atypical responders(5 prolonged immediate, 6 square-shaped, 1 progressive). Four(9%) subjects had negative results on the methacholine bronchial challenge test. High levels of serum specific IgE antibody to isocyanate-HSA were found in 17(40%) patients. The prevalence of a specific IgE antibody was not associated with a type of TDI-bronchial challenge test response, smoking and atopic status, presence of rhino-sinusitis and systemic symptoms, or a degree of airway hyperresponsiveness to methacholine(p> 0.05). The period of latency, ranging from 3 to 132 months, was significantly longer in high specific IgE responders (p< 0.05). These data suggest that 40% of isocyanate-induced occupational asthma patients had high specific IgE antibody to isocyanate-HSA conjugate. The presence of specific IgE antibody does not seem to correlate with clinical parameters.